There is heterosis such that a hybrid has a considerable improvement in biomass, pest and disease resistance, stress (drought, high temperature, low temperature, saline-alkali soil, etc.) resistant capability over its parents; for example, hybrid corn (zea mays) or hybrid rice has a much greater production yield than homozygous parents thereof. A method often used for producing a hybrid comprises: growing a female parent and a male parent together, removing tassels of the female parent, while retaining tassels of the male parent, and harvesting seeds of the female parent as a hybrid.
There are three types of self-pollination, cross-pollination and often cross-pollination for plants in nature. Self-pollination refers to a phenomenon where gynoecia of a plant are pollinated with pollen from the same plant. Among plants with a hermaphrodite flower, it may be classified into autogamy in which pollination occurs between stamen and pistil of a single flower (phaseolus); gei-tonogany in which pollination occurs between different followers in the same inflorescence (individual); and close pollination in which pollination occurs between different followers in the same plant. Some plants have stamen and pistil grown not in the same flower, even not in the same plant, incapable of self-pollination, and their pistil can merely receive pollen from other flower—this is called cross-pollination. A type of crops that has a natural hybridization rate of greater than 50% and declined selfing is classified into often cross-pollinated crops, such as corn.
Corn is an androgynal plant, and has female and male flowers at different positions of a plant. Corn can propagate via self-pollination or cross-pollination, and finish its natural pollination when pollen is blown from tassels to filaments of female ears in natural conditions.
In breeding of corn, a self-bred line of homozygous corn should be first developed, then two self-bred lines are crossed, and the progenies thereof are assessed for yield, resistance, etc., to determine the presence of a commercialization potential or not. Therein, each of the self-bred lines may have one or more good traits of which another self-bred line lacks, or complement one or more poor traits another self-bred line has. Hybridization of two self-bred lines results in a seed of a first generation, called the F1 seed, which is germinated to obtain a F1 plant. The F1 plant is stronger than both of parental (paternal and maternal) self-bred lines, while simultaneously having greater biomass.
A hybrid may be produced by artificial emasculation of the female parent, i.e., removal of tassels of un-pollinated female parents (which may be sown in a field alternated with the male parent, for example, by sowing 5 rows of the female parent with 1 row of the male parent), remaining tassels of male parents. Subsequently, with only an isolation of foreign corn pollen, female ears of the female parent may merely receive pollen from the male parent, to obtain a seed, i.e., a hybrid seed (F1). Such hybrid seeds may be used for agricultural production.
In the production of the hybrid seeds, a plant may be tassellized again after emasculation due to a change in environment, or may be incompletely emasculated, both of which may lead to a self-pollination of the female parent, so that produced hybrid seeds have the seeds from the maternal self-bred line blended. The yield of the maternal self-bred line is much lower than that of the hybrid seed, and such a seed is an unqualified product, which will have an adverse impact on the income of a farmer and on the credit of a seed producing company, and more severely the seed producing company will have to assume corresponding liability to pay compensation.
Machines may also be used for emasculation of the female parent, emasculation by machine is reliable substantially the same as manual emasculation, but faster and with lower costs. However, in comparison with manual emasculation, most of machines for emasculation will make more damage on a plant. For this reason, there is no means completely satisfied for emasculation by now, and there is still a need of an alternating method with lower costs and more complete emasculation.
A stable male sterility system provides a simple and effective method, and onerous emasculation may be obviated in some genotypes by using a nucleo-cytoplasmic interacting male sterile (CMS) self-bred line. This method comprises three main materials, i.e., a sterile line: a male sterility material; a maintainer line: capable of providing pollen to the sterile line, allowing progenies of the sterile line still to be a sterile line, a restorer line: capable of restoring fertility of a sterile line. The sterile line is crossed with the restorer line to produce F1, i.e., a hybrid seed used for agricultural production. More particularly, a nucleo-cytoplasmic interacting sterility type is characterized by heredity of nucleo-cytoplasmic interaction. It is required not only that the cytoplasma has a sterility gene S, but also that the nucleus has a homozygous sterility gene (rfrf), and only in the presence of both, a plant may exhibit male sterility. If the cytoplasmic gene is a fertile N, the plant will exhibit male fertility regardless of fertility (RfRf) or sterility (rfrf) of the nucleic gene. Similarly, if the nucleus has a fertility gene (RfRf) or (Rfrf), the plant will exhibit male fertility regardless of fertility N or sterility S of the cytoplasmic gene. Such a male sterile line formed from a nucleo-cytoplasmic interaction is genetically composed of S (rfrf), which cannot produce normal pollen, but can parent for hybridization. Since a maintainer line N (rfrf) [which is used to cross with a sterile line to produce F1 that is still able to maintain male sterility, that is: S (rfrf) (♀)×N (rfrf)→S (rfrf) (sterility)] may be found and may receive pollen from a restorer line S(RfRf) or N(RfRf) [which is used to cross with a sterile line to produce F1 that is fertile, that is: S (rfrf) (♀)×S (RfRf)→5 (Rfrf) (F1) (fertile), or S (rfrf) (♀)×N (RfRf)→S (Rfrf) (F1) (fertile)], to restore F1 to be male fertile, F1 plant may be self-bred to generate F2. Therefore, this may be widely used in agricultural production. The use of male sterile line may avoid manual emasculation, save manpower and reduce seed cost, and guarantee purity of seeds. Currently, nucleo-cytoplasmic interacting male sterility has been used for the production of hybrid seeds in crops such as rice, corn, sorghum, onion, castor, sugarbeet and rape; for the nucleo-cytoplasmic interacting male sterile line of additional crops, wide studies are also on the way.
CMS system also has its drawbacks. One is an observation that individual CMS materials are susceptible. Another one is difficulty in finding restorer line. These problems prevent wide use of the CMS system in seed production.
U.S. Pat. Nos. 4,654,465 and 4,727,219 to Brar et al. disclose a type of genetic sterility. However, this type of genetic sterility requires maintaining of corresponding genotypes at a number of different sites within a genome, and labeling, tracing and detecting of these sites in each generation. Patterson also describes a possibly useful chromosomal translocation gene system, however, this system is more complex (see U.S. Pat. Nos. 3,861,709 and 3,710,511).
People have been trying to optimize the male sterility system. For example, Fabijanski, et al. developed a method of making a male sterile plant (EPO 89/3010153.8 with a Publication No. 329308 and PCT Application No. PCT/CA90/00037 published as WO 90/08828). Fertility of a male flower of a plant is inhibited primarily by following two methods. One is to link a promoter specifically expressed by a male tissue to a cytotoxic gene and transplant it into a plant, so that the male flower cannot pollinate as normal and does not affect other traits; the other is, by gene interfering means, to interfere a cloned gene for regulating male flower fertility of a plant in a transgenic way, so that it is not capable of normally functioning. Additionally, there are means to inhibit gene expression through some gene regulatory elements, so as to affect fertility of a plant (WO90/08829).
In most cases, only a plant with a male sterility regulatory nuclear gene that is homozygous recessive (msms) will exhibit male sterility. Since a male sterile plant is not capable of selfing, the male sterile plant (msms) may be obtained only by its cross with a heterozygous plant (Msms). And, there are both of male sterile grains (msms) and fertile heterozygous grains (Msms) on the same ear, from which it is impossible to distinguish which are sterile grains, and which are fertile grains. Those may be distinguished only at the time of pollination of the plant after sowing.
Recently, transgenic methods are also used to keep sterility of a male sterile plant (U.S. Pat. No. 6,743,968). Such methods construct a pollen lethal gene and a male fertility restorer gene into a single vector, and introduce it into a male sterile plant. Transgenic progenies exhibit fertility, but having only ability of producing pollen free of a restorer gene. When such a plant is crossed with a male sterile plant, a recessive sterile plant is maintained in a homozygous recessive state. First, a transgenic vector is constructed, which contains a pollen cell lethal gene and meanwhile a dominant gene of restoring plant fertility. The vector is introduced into a male sterile plant, and is present in the transgenic plant in a heterozygous state. The plant is fertile due to the presence of the fertility restorer gene, and when it is crossed with a male sterile plant, pollen (Msms) containing both of a restorer gene and a lethal gene results in pollen abortion. Therefore, only the pollen (ms) containing no restorer gene can be crossed with a female gamete (ms) of a male sterile plant, and each of the progenies is a homozygous recessive individual (msms).
As previously described, an important problem in many attempts for seed production with a male sterility system is how to use the male sterility gene and how to distinguish a male sterile seed and a fertile seed, while considering how to maintain the sterility of a sterile individual.
Many male sterile mutants have been identified in corn (Skibbe et al. 2005), particularly as seen in the table below:
TABLE 1Male sterile mutants resulted from a nuclear geneMutant(alleleicmutation)ChromosomeReferencesms16Singleton W. R and Jonnes D. F.1930. Heritable characters of maize. XXXV.Male sterile. J Hered 21: 266-268ms29Eyster W. H. 1931. J Hered 22: 99-102;ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms33Eyster W. H. 1931. J Hered 22: 99-102ms4(po1)BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431ms55BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431;ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms6(po1)BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431;ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms77BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431;ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms88BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431;ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms91BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431;ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms1010BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431;ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms1110BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431;ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms121BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431;ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms135BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431;ALBERTSEN M. C.,R.L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms141BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431;ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms15BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431ms16BEADLE G. W., 1932. GENES IN MAIZE FORPOLLEN STERILITY. GENETICS17: 413-431ms171EMERSON R. A., 1932. A recessive zygoticlethal resulting in 2:1 ratios for normal vs.male-sterile and colored vs. colorless pericarpin F2 of certain maize inbreds. Science 75:566; ALBERTSEN M. C.,R. L. PHILLIPS, 1981. Developmental cytologyof13 genetic male sterile loci in maize. Can. J.Genet. Cytol. 23: 195-208ms181EYSTER W. H., 1934. Genetics of Zeamays. Bibliogr. Genet. 11: 187-392ms199EYSTER W. H., 1934. Genetics of Zeamays. Bibliogr. Genet. 11: 187-392ms20EYSTER W. H., 1934. Genetics of Zeamays. Bibliogr. Genet. 11: 187-392Ms216SCHWARTZ D., 1951. The interaction ofnuclear and cytoplasmicfactors in theinheritance of male sterility in maize.Genetics36: 676-696ms227WEST D. R., M. C. ALBERTSEN, 1985. Three(msca1)new male-sterility genes. Maize Genet. Coop.Newsletter 59: 87; TRIMNELL M. R., T. W.FOX, M. C. ALBERTSEN, 2001 Newmale-sterilemutant allele of Ms22.Maize Genet. Coop. Newsletter 75: 31;CHAUBAL R., J. R. ANDERSON, M. R.TRIMNELL, T. W. FOX, M. C. ALBERTSEN, P.BEDINGER, 2003. The transformation ofanthers in themsca1 mutant of maize. Planta216: 778-788ms23WEST D. R., M. C. ALBERTSEN, 1985. Threenew male-sterility genes. Maize Genet. Coop.Newsletter 59: 87; CHAUBAL R., C.ZANELLA, M. R. TRIMNELL, T. W. FOX, M. C.ALBERTSEN, P. BEDINGER, 2000. Twomale-sterile mutants of Zea mays (Poaceae) withan extra cell division in the anther wall.Am. J. Bot. 87: 1193-1201ms2410WEST D. R., M. C. ALBERTSEN, 1985. Threenew male-sterility genes. Maize Genet. Coop.Newsletter 59: 87; FOX T. W., M. R.TRIMNELL, M. C. ALBERTSEN, 2002.Male-sterile mutant ms24 mapped tochromosome 10. MaizeGenet. Coop. Newsletter 76: 37ms259LOUKIDES C. A., A. H. BROADWATER, P. A.BEDINGER, 1995. Two newmale-sterilemutants of Zea mays (Poaceae) withabnormaltapetal cell morphology. Am. J. Bot.82: 1017-1023ms261LOUKIDES C. A., A. H. BROADWATER, P. A.BEDINGER, 1995. Two newmale-sterilemutants of Zea mays (Poaceae) withabnormaltapetal cell morphology. Am. J. Bot.82: 1017-1023ms27ALBERTSEN M. C., 1996. Ms-genedesignations. Maize Genet. Coop. Newsletter70: 30-31ms281GOLUBOVSKAYA I. N., D. V. SITNIKOVA,1980. Three meiotic mutations of maize,causing irregular segregation ofchromosomesin the first division of meiosis.Genetika 16: 656-666ms2910TRIMNELL M. R., T. W. FOX, M. C.ALBERTSEN, 1998. New chromosome10S male-sterile mutant: ms29. MaizeGenet. Coop. Newsletter 72: 37-38ms304TRIMNELL M. R., T. W. FOX, M. C.(msx)ALBERTSEN, 1998. New chromosome 2Lmale-sterile mutants ms30 and ms31. MaizeGenet. Coop. Newsletter 72: 38ms312TRIMNELL M. R., T. W. FOX, M. C.ALBERTSEN, 1998. New chromosome 2Lmale-sterile mutants ms30 and ms31. MaizeGenet. Coop. Newsletter 72: 38ms322CHAUBAL R., C. ZANELLA, M. R. TRIMNELL,T. W. FOX, M. C. ALBERTSEN, P.BEDINGER, 2000. Two male-sterilemutants of Zea mays(Poaceae) with anextra cell division in the anther wall. Am. J.Bot. 87: 1193-1201ms332TRIMNELL M. R., E. PATTERSON, T. W.FOX, P. BEDINGER, M. C. ALBERTSEN,1999. New chromosome 2L male-sterilemutantms33 and alleles. Maize Genet. Coop.Newsletter 73: 48-49ms347TRIMNELL M. R., E. PATTERSON, M. C.ALBERTSEN, 1999. New chromosome7L male-sterile mutant ms34. MaizeGenet. Coop. Newsletter 73: 49ms35TRIMNELL M. R., E. PATTERSON, T. W.(ms23)FOX, M. C. ALBERTSEN, 1999. Newchromosome 9L male-sterile mutantsms35 and ms36. Maize Genet. Coop.Newsletter 73: 49-50; TRIMNELL M. R., T. W.FOX, M. C. ALBERTSEN, 2002. We made amistake! ms35 is alleleic to ms23, but what isthe correct map location? Maize Genet. Coop.Newsletter 76: 37-38; ALBERTSEN M. C.,T. W. FOX, M. R. TRIMNELL, 1999. Changinga duplicated designation for two differentmale-sterile mutationsMaize Genet. Coop.Newsletter 73: 48ms369TRIMNELL M. R., E. PATTERSON, T. W.FOX, M. C. ALBERTSEN, 1999. Newchromosome 9L male-sterile mutantsms35 and ms36. Maize Genet. Coop.Newsletter 73: 49-5ms373TRIMNELL M. R., T. W. FOX, M. C.ALBERTSEN, 1999. New chromosome3L male-sterile mutant ms37. MaizeGenet. Coop. Newsletter 73: 48ms382TRIMNELL M. R., T. W. FOX, M. C.(ms*WL89A)ALBERTSEN, 1998a New chromosome10S male-sterile mutant: ms29. MaizeGenet. Coop. Newsletter 72: 37-38;ALBERTSEN M. C., T. W. FOX, M. R.TRIMNELL, 1999. Changing a duplicateddesignation for two different male-sterilemutationsMaize Genet. Coop. Newsletter 73:48Ms414NEUFFER M. G., 1987. Location of dominantmale sterile on chromosome 4L. Maize Genet.Coop. Newsletter 61: 51Ms425ALBERTSEN M. C., T. W. FOX, M. R.TRIMNELL, M. G. NEUFFER,1993. Interval mapping a new dominantmale-sterile mutant, Ms42. Maize Genet.Coop. Newsletter 67: 64ms438GOLUBOVSKAYA I. N., 1979 .Geneticalcontrol of meiosis. Int. Rev. Cytol. 58: 247-290Ms444ALBERTSEN M. C., L. M. SELLNER,1988. An independent, EMS-induceddominant male sterile that mapssimilar to Ms41. Maize Genet. Coop.Newsletter 62: 70; ALBERTSEN M. C., M. G.NEUFFER, 1990. Dominant male sterileinmaize. Maize Genet. Coop. Newsletter 64:52ms459ALBERTSEN M. C., M. R. TRIMNELL, T. W.FOX, 1993. Tagging, cloningandcharacterizing a male fertility gene in maize.Am. J. Bot. 80: 16ms4710TRIMNELL M. R., T. W. FOX, M. C.ALBERTSEN, 2002. New chromosome10 male-sterile mutant: ms47. MaizeGenet. Coop. Newsletter 76: 38ms489TRIMNELL M. R., T. W. FOX, M. C.ALBERTSEN, 2002. New chromosome 9Lmale-sterile mutant: ms48. MaizeGenet. Coop. Newsletter 76: 38ms4910TRIMNELL M. R., T. W. FOX, M. C.ALBERTSEN, 2002. New chromosome 10male-sterile mutant: ms49. MaizeGenet. Coop. Newsletter 76: 38-39ms506TRIMNELL M. R., T. W. FOX, M. C.ALBERTSEN, 2002e New chromosome6L male-sterile mutant: ms50. MaizeGenet. Coop. Newsletter 76: 39ms5210Skibbe D S, Schnable P S: Male sterility inmaize. Maydica 2005, 50: 367-376
These genes as above have been successively cloned, e.g., ms45 (Albertsen et al. 1993) and ms26 (PTC/US2006/024273). Meanwhile, some male sterility genes from rice also have been successively cloned, e.g., dpw (Jing Shi et al. 2011), and some male sterility genes, e.g., (Aarts, et al. 1993) have been identified in Arabidopsis. 